This invention concerns apparatus for processing product, wherein the product is heated to an elevated temperature, and while heated subjected to a nonatmospheric gas environment, whereby the physical characteristics of the product are changed by the process. The apparatus may be employed, for instance, in producing an oxide coating as a surface layer on silicon wafers, although in describing this particular use, it is not intended thereby to limit the invention, as obviously the apparatus may be employed in other processes where heating with a controlled gaseous environment is required.
In the semiconductor manufacturing industry, it is a common practice to produce an oxide coating on wafers, normally of silicon, with these wafers then being employed in the production of integrated circuits. To produce an oxide coating on such wafers, it is conventional to mount a plurality of the wafers on a support, sometimes referred to as a boat, and then to move the boat together with the wafers supported thereby into an oven. The oven is purged of atmospheric gas and a processing gas introduced, with the processing gas selected being dictated by the type of oxide coating which is desired in the final product. With heating of the oven containing the wafers and the processing gas, the oxide coating is produced. After coating, the oven is purged of processing gas and the load of coated wafers permitted to cool.
To prevent contamination, it is conventional to employ, as the means defining the oven for the treatment of the wafers, an elongate quartz glass tube. A tube of this description is capable of being thoroughly cleaned and the quartz glass forming the tube is substantially completely inert under the operating conditions employed. To produce coated wafers of consistent quality, it is important that techniques be utilized which effectively prevent any dust or other foreign matter from being introduced into the oven during the oxidation process.
One form of apparatus that has been employed in the past in the preparation of oxide coatings includes what is commonly referred to as an elongate cantilever which has a distal or unsupported end and an opposite mounted end. The mounted end referred to is mounted for movement in an elongate path, with movement in one direction being operable to thrust the distal end of the cantilever into the quartz tube forming the oven and movement in the opposite direction serving to retract the distal end of the cantilever. With a boat or other means supporting wafers mounted on the cantilever's distal end, and with a door mounted on the cantilever effective to close off the oven tube with the distal end fully inserted, means is provided for inserting the wafers into the oven and for closing the oven, with the elimination of any rollers or other slide support for the boat within the oven which would tend to produce dust and result in contamination The cantilever system is fairly widely used, but has a serious disadvantage when employed in the production of coated wafers since it is difficult, rapidly and efficiently, to cool the wafers after the coating process without contamination. If the cantilever described is retracted from the tubular oven and with the wafers still hot, the wafers while in this hot state are exposed to the atmosphere, and contamination results.
In another form of equipment, a so-called elephant is employed which is an elongate, hollow, normally quartz tube that is mounted in a position with an end of the tube in registry with the open end of the oven tube, thus to close off the open end of the oven tube. A boat or other means movable within the elephant tube is shifted to transfer a load of wafers into the oven tube. The elephant tube provides a chamber where cooling can take place together with purging, which is outside the furnace. However, the use of the boat introduces a problem of dust and resultant contamination. Furthermore, if the elephant tube is to be purged of processing gas, such is done through an opening at the end of the tube remote from the oven. With many processing gases being highly noxious, proper ventilation and the safety of personnel operating the equipment become a problem.
A general object of this invention is to provide novel apparatus for processing product at an elevated temperature and in a nonatmospheric gas environment, which features a walled assembly having a depository chamber defined within the assembly, product being movable into the chamber during cooling.
Another object is to provide such apparatus with improved means for channeling gas therethrough, as when purging the apparatus of atmospheric gas and introducing into the apparatus a processing gas.
A further general object is to provide apparatus for processing product at an elevated temperature and for then cooling the product, constructed in such a manner as to minimize contamination problems characterizing prior art equipment.
In a preferred embodiment of the invention, a walled assembly is provided having within it a depository chamber for receiving product during cooling of the product. A cantilever having a distal end for supporting product extends into the depository chamber. The assembly is movable to be placed against an oven opening when the product is heated, and the cantilever is movable in a path paralleling that of the walled assembly to move the product into the oven.
A more specific object of the invention is to provide such a walled assembly which includes a pair of concentric tubes, and there being a space between the tubes providing for the channeling of gas. The inner wall of the inner tube defines a depository chamber, and the space between the concentric tubes is utilized to channel gas traveling through the depository chamber back to a zone where a means for scavenging gas is provided. With the concentric tube assembly mounted for movement toward and away from the open end of an oven tube, the gas scavenger means may conveniently be located adjacent this open end of the oven tube, and the space between the tubes utilized to return gas traveling down the concentric tube assembly to the region where the scavenger means is located.